Effect of Molecular Symmetry and Intermolecular Halogen‐Halogen Interactions on the Crystal Structures of Halogen‐Substituted Benzoic Acids. X‐ray Crystal Structure of m‐Iodobenzoic Acid

Abstract

The crystal structure of m‐iodobenzoic acid is reported. The crystals are monoclinic, P21/c, with a = 6.220(3) Å, b = 4.689(2) Å, c = 26.67(1) Å, β = 101.80(3)°, Z = 4, C7H5IO2. The structure has been determined by direct methods and refined to R 0.026 for 1288 reflections recorded with an automatic single crystal diffractometer. The structure is composed of essentially planar hydrogen‐bonded dimer units with significant intermolecular iodine‐iodine contacts. The configuration of the dimer unit is transoid. Since this is the penultimate member of the family of mono‐halogen‐substituted benzoic acids its structure is compared with those previously reported. In particular, the effects of differences in molecular geometry of the o‐, m‐, and p‐isomers and the strengths of the intermolecular halogen‐halogen interactions are surveyed. The geometry of the carboxyl group of m‐iodobenzoic acid in the solid state and the carbonyl absorption in the Ftir spectrum of the crystalline acid at room temperature suggest the presence of dynamic proton isomerism as has been recently found by other investigators in crystalline benzoic acid and some of its derivatives.

Packing Modes in Some Mono‐ and Disubstituted Phenylpropiolic Acids: Repeated Occurrence of the Rare syn,anti Catemer

“…Indeed, it has the very rare cisoid configuration, which is generally disfavored when compared to the transoid configuration on energetic and packing grounds. The possibility of a cisoid configuration for dimers of unsymmetrically substituted aromatic acids was first raised by Patil et al., who wrote that “in spite of the seeming rarity of the cisoid configuration, it is likely that m ‐substituted benzoic acids, under suitable conditions, may be induced to crystallize in polymorphic forms composed of acid dimers in the cisoid arrangement.”52 For example, m ‐nitrobenzoic acid is dimorphic with a stable transoid and an unstable cisoid form. Two features of the crystal structure of acid 2 d are then notable: 1) it is the first example of an ortho ‐substituted acid to show the cisoid configuration; 2) the acid is not polymorphic, at least not as far as we were able to conclude after the several attempts we made in this direction.…”

“…The possi-bility of a cisoid configuration for dimers of unsymmetrically substituted aromatic acids was first raised by Patil et al, who wrote that "in spite of the seeming rarity of the cisoid configuration, it is likely that m-substituted benzoic acids, under suitable conditions, may be induced to crystallize in polymorphic forms composed of acid dimers in the cisoid arrangement." [52] For example, m-nitrobenzoic acid is dimorphic with a stable transoid and an unstable cisoid form. Two features of the crystal structure of acid 2 d are then notable: 1) it is the first example of an ortho-substituted acid to show [a] The data for 4 a-f, which are discussed herein, have been published previously.…”

Structure of 4-iodo-trans-cinnamic acid and a study of carboxyl group disorder

“…Perhaps Type II is favoured because I is more polarizable. A case in point is the I-.-I contact of 3.985/~ in 3-iodobenzoic acid, a compound whose crystal packing (Patil, Curtin & Paul, 1984) shows many features in common with that of the title compound.…”

Halogen bonds in some dihalogenated phenols: applications to crystal engineering

“…The situation is more complicated in that while polarizability is more important for I , anisotropy is significant for Cl. The study carried out by Miller, Paul and Curtin on halogen-substituted acids and anhydrides showed that in 4-chlorobenzoic acid, acid dimers are connected through type I ClÁ Á ÁCl contacts, whereas in 4-iodobenzoic acid, I Á Á ÁI contacts are type II (Miller et al, 1974;Patil et al, 1985). This early observation indicates that the likelihood of formation of type II contacts increases from Cl to I .…”